Manufacturing operations often employ machine tool systems to form the various constituent parts in a desired product. Briefly, a machine tool system is operable to process a workpiece that is fixedly retained at a process station within the system according to a predetermined set of instructions. During the processing, a machine tool retained by the system engages the workpiece and removes predetermined amounts of the material from the workpiece. A new surface is thus generated on the workpiece that conforms more closely to the desired final shape of the part. Examples of processes that may be performed by machine tool systems include drilling, reaming, milling planar and/or curved surfaces, and turning a workpiece about a fixed axis, in addition to other known machining operations.
The process station generally includes a workpiece jig that supports the workpiece within the process station so that the workpiece is suitably oriented relative to the one or more machine tools operably controlled by the machine tool system. In many cases, the workpiece jig is configured to support the workpiece in more than one position relative to the machine tools so that a first set of machined features are formed on the workpiece when positioned in a first position, and a second set of machined features are formed when positioned in a second position. Depending upon the complexity of the workpiece, the workpiece jig may include still other additional positions.
With reference now to FIG. 1, a plan view of a workpiece 10 retained in a process station 12 is shown, according to the prior art. The workpiece 10 is positioned on a workpiece jig 14 having a set of dowel pins 16 that are removably received by location holes 18 that project through the workpiece 10. The workpiece 10 faces a machine tool (not shown in FIG. 1) that is configured to form the first set of machined features on the workpiece 10 (also not shown in FIG. 1). The workpiece 10 is then removed from the workpiece jig 14 and rotated about an axis 20 so that an opposing side of the workpiece 10 faces the machine tool when the location holes 18 re-engage the dowel pins 16. A second set of machined features (also not shown in FIG. 1) are then formed on the opposing side of the workpiece 10.
A significant drawback associated the foregoing method is that positional differences between the first set of machined features and the second set of machined features may be introduced into the workpiece 10 due to positional errors present in the workpiece jig 14. As shown in FIG. 1, the positional errors result in shifting the workpiece 10 in a first direction Δx and a second direction Δy following the rotation of the workpiece 10. Accordingly, the first set of machined features and the second set of machined features in the finished part are correspondingly offset by the positional values Δx and Δy. The positional errors may be introduced, for example, by errors in positioning the dowel pins 16 during fabrication of the jig 14, or they may be introduced as the dowel pins 16 are subjected to wear, or by still other variations in the jig 14. Accordingly, improved methods for controlling dimensional variations introduced into workpieces by dimensional variations in the workpiece jig, or by other means, would have utility.